Vapor phase substitution fluorination of aromatics with xenon difluoride

ABSTRACT

THE PROCESS OF PRODUCING A FLUORINE-SUBSTITUTED AROMATIC COMPOUND IN THE VAPOR PHASE WITH XENON DIFLUORIDE MATIC AT A MODERATE TEMPERATURE ON THE ORDER OF ABOUT VAPOR COMPOUND IN THEVAPOR PHASE WITH XENON DIFLUORIDE 200*C. AT A MOLE RATIO OF XENON DIFLUORIDE TO SAID AROMATIC COMPOUND OF NO GREATER THAN 1.

vAron PHASE SUBSTITUTION Fin-amines F AROMATICS wrrn XENON DIFLUORIDE Donald R. MacKenzie, Bellport, Jack Fajer, Brookhaven, and Robert Smol, East Patchogue, N.Y., assignors to the United States of America as represented by the Y United States Atomic Energy Commission No Drawing. Filed July 23, 1971, Ser. No. 165,591"

Int. Cl. C07c 25/00; C07d 51/76 US. Cl. 260-250 R' 2 Claims ABSTRACT on THE DISCLOSURE The process of producing a fluorine-substituted aromatic compound comprising the step of reacting an aromatic compound in the vapor phase with xenon difluoride vapor at a moderate temperature on the order of about 1 200 C. at a mole ratio of xenon difluoride to said aromatic compound of no greater than 1.

SOURCE OF THE INVENTION Fluorinated aromatic compounds have attracted interest in recent years because of their great stability in a reactor environment as coolants and as high temperature heat transfer mediums. The fully saturated compound is less stable, apparently due to the alteration of the aromatic structure during fluorination.

By fluorinated aromatic compound is meant an aromatic compound in which only the hydrogen atoms present are replaced by fiuorine atoms. This compound is also referred to as a fluorine-substituted aromatic compound.

The production of fluorine-substituted aromatic compounds has been accomplished by utilizing XeF in liquid CCL; solution and carrying out the substitution at low temperatures, such as 70 C. After substitution, the solvent is removed.

The liquid fluorine substitution process just described while useful is somewhat slow and requires the removal of the solvent before the fluorinated aromatic compounds can be used.

SUMMARY OF THE INVENTION The present invention improves upon the previous described process for the production of fluorine-substituted aromatics from aromatics, substituted aromatics, heterocyclic aromatics, and fused-ring aromatics by conducting the substitution with the reactants in the vapor state, without the presence of any solvents.

In accordance with this invention, XeF vapor is added to a closed reactor vessel containing the liquid or solid aromatic compound at ambient pressure and temperature at a mole ratio of XeF to said aromatic compound no greater than one, heating the reactor vessel and its contents until the compound is vaporized, and after a period of a few minutes to permit the fiuorination process to occur, cooling the vessel to freeze the fluorinated aromatic compound so as to permit pumping off the gaseous un wanted products.

It is thus a principal object of this invention to prepare fluorine-substituted aromatic compounds at a moderate temperature and free of solvents.

Other objects and advantages of this invention will hereinafter become evident from the following description of preferred embodiments of this invention.

, H E rQpIMeNreg I .In accordancekwith a preferred embodiment of this invention, the liquid or solid aromatic compound is .placed into a closed reactor vessel,-the air is evacuatedyand XeF vapors are'trausferredvinto the reactor vessel. The vessel is then-heated until-the-aromatic compound is completely in the vapormhase'aAfter a -few-minutes during which time the XeF and aromatic vapors react, the vessel is cooled to -78 C. whenthe vessel is evacuated to remove the HF and Xe. The temperature is raised to ambient and the fluorinated aromatic compound in the vessel may be removed for use or storage.

It will be noted that the fluorination takes place rapidly under the conditions described. The organic compounds are those which are obtained commercially and are pure enough to be used as received. Aromatic compounds which have been .used successfully in accordance with this invention include benzene, nitrobenzene, o-, mand p-difiuorobenzene, 2-fiuoropyridine, pyrazine, 1,3,5-tritertiarybutylbenzene, benzaldehyde, and naphthalene.

The following examples illustrate this invention:

EXAMPLE 1 XeF was prepared by the known method of exposing xenonfiuorine mixtures to sunlight in a glass bulb and stored in crystalline form in evacuated nickel alloy U- tubes. 217 mg. XeF and 215 l. commercially obtained benzene were transferred under vacuum into a prefluorinated reaction vessel of 150 cc. volume forming a closed system. The vessel was heated to a temperature of 145 C. to ensure that the reactants were in the vapor phase. After after two minutes at the elevated temperature to permit the reaction to be completed, the vessel was cooled with Dry Ice to 78 C., and HF and xenon were pumped off. The HP and xenon may be recovered for reuse if desired. The organic products were transferred under vacuum to a glass container where the fluorinated benzene was analyzed by gas-liquid chromatography. 50% of the fluorine is available for fiuorination (the remainder going to HF) and of that it was discovered that about 60 mole percent yield was obtained.

The chemical process taking place for benzene is as follows:

Some of the C H F proceeds to 0-, m-, and p-difluorobenzene.

EXAMPLES 2-10 The procedure followed in the preceding example was carried out using instead of benzene the aromatic compounds nitrobenzene, o-, m-, and p-difluorobenzene, 2- fluoropyridine, pyrazine, 1,3,5 -tritertiary-butylbenzene, beuzalclehyde, and naphthalene.

For naphthalene, 376 mg. were reacted with 221 mg. XeF and heated to a temperature of 200 C. With 2- fiuoropyridine, in a 1.5 liter vessel, 3 cc. of the organic compound was reacted with 1.130 g. XeF at a temperature of C. The other reactions were similarly conducted.

In each case the vessel was heated to sufficient temperature to volatize the compound, the boiling point for each of the reactants varying somewhat. Yields in all cases were similar or comparable to that obtained with the benzene.

From the various examples it is concluded that vapor phase reactions with XeF, leads to facile, easily controlled substitution of aromatic compounds. The method offers advantages in the ease of preventing overreactions which occur in solution as well as being more economic and faster than previously known methods.

' 1. In a method of producing a fiuorifi derii'itive aromatic compound by steps flinch include reacting in a closed tqrtyssvss s v 2 equ mq smm um of an aromaticcor'npouxid'ian 5 er'ein' 'siid 'itromatic compound is selected "from'the group consisting of ben- 'ze'ne, nitrobenzeiie; znd'p-difiuorobenzne; Z fiudropyridine, pyrazine', '1 ,3:,5-tnitertiary btitylbenzeneg- *ben'za'ldehyde; 3nd "naphthalene, "the. improvement which-"comprises producing the fluorine "derivative by th'esubsti'tution' reaction by: heating itheareactor i vessel to 1 cause ra'icfiOfl bQt-Weefi XeFyandwhid aromatiwcompound in the vaporphase.

2. The method of claim 1 in which the fluorinated compound following completion of the reaction is frozen to permit the removal of Waste gaseous products.

References Cited UNITED STATES PATENTS 3,694,444 9/1972 Klauke 260-251 2,533,132 12/1950 McBee et a1. 260-653 V T MW FOREIGN PATENTS. 1,163,582 9/1969 Great Britain 260250 A OTHER REFERENCES Shaw, M. I. et al.: Reqctipn of Xenon Difluoride With Aromatje Compounds}; L'AQC S 197 O 9 2(22 649.8-

1.15 l TLC-Net hLzRmzWk enon F ludr iiies' With {OrganicCOmpdzmdsJ 'OIgL Chem; 1970, (12); 4.020- t 24 I R. D. McCLOUD, Assistant Examiner 'j -X-R-;. v 2'60-290 HL, 599, 646, 650 F, 651 F, 694; 423-462 

